Currently, a large power output is demanded for AC generator for vehicle, making a key issue in improving a cooling ability for a rectifier located therein, which generates a large amount of heat by a large current flowing therethrough. It is considered to raise an ability of fans for cooling the rectifier, however, this increases a noise of the fans. Thus, to secure a vehicular compartment against noise, it is not always appropriate to raise the cooling ability of the fans.
JP-2001-037142-A and U.S. Pat. Nos. 6,184,602 and No. 5,949,166 (JP Patent No. 3438577) disclose AC generators having an opening for inducing outer air to flow through an air passage between a rear frame and a protection cover as a cooling wind and to hit on a holder fin, which locates a rectifier thereon, so as to cool the rectifier.
However, according to the above public knowledge, the air passage is formed at rear side of the holder fin, so that the rectifier is not directly disposed to the cooling wind and not sufficiently cooled. Further, a clearance forming the air passage between the rear frame and the holder fin is narrow, so that muddy water, which may cause an erosion, stays therein.